(62aw) The Development of Bacterial Resistance to Silver Dressings

Silver, in the form of AgNO3, has been used as an antimicrobial agent for the last 125 years. Initially it was delivered as a 1% AgNO3 solution (6352 mg/L) but over the years this was reduced to a 0.5% AgNO3 solution (3176 mg/L) that was applied up to 12 times per day. In 1967, 1% silver sulfadiazine cream (3025 mg/kg) was introduced, and it became the standard therapeutic treatment for burns world wide. More recently, new silver dressings have entered the medical marketplace. These dressings often release less than 5 mg/L of silver. Nadworny (personal communication) has shown that organisms such as Pseudomonas aeruginosa readily develop resistance to silver when exposed to successively higher doses of silver. They do not readily develop resistance to single high doses of silver (>3000 mg/L). This raises concerns about the appropriateness of using silver dressings which release low doses of silver. In this study, we examined the ability of clinically relevant bacteria to develop tolerance/resistance to silver released from commercially available silver-containing dressings. The results showed that bacteria could develop resistance to low dose silver dressings after repeated exposures. This is a significant concern for patients treated with dressings, which contain inappropriate levels of silver.